1. Field of the Invention
The present invention relates to a terminal structure which is applied to a connector such as a female connector corresponding to a male connector, a connector for a flat cable or the like.
2. Related Art
Heretofore, there has been commonly known a terminal structure of the above mentioned female connector and the connector for the flat cable which is so constructed that an elastic tongue piece having a contact is disposed in an engaging part in a cylindrical shape in which a male side conductor including a male terminal or a flat cable is adapted to be engaged, and the contact of the tongue piece can be elastically press contacted with the male side conductor to be engaged in the engaging part.
FIG. 6 shows several examples of the structures of the conventional female terminals. A female terminal 101 which is shown in FIG. 6A has an engaging part 102 in a cylindrical shape in which a male terminal (male tab) 100 can be engaged, and a tongue piece 103 whose base end portion 103b is continued from a forward end of a lower wall of the engaging part 102 and folded backward therefrom. The tongue piece 103 has a crooked portion in an angled shape to form a contact 103a at an apex of the angled shape.
A female terminal 111 which is shown in FIG. 6B has an engaging part 112 in a cylindrical shape in which the male terminal 100 can be engaged, and a tongue piece 113 whose base end portion 113b is continued from a backward end of a lower wall of the engaging part 112 and cut out therefrom to extend diagonally forward in an erected manner. A contact 113a is provided near a forward end of the tongue piece 113.
A female terminal 121 which is shown in FIG. 6C has an engaging part 122 in a cylindrical shape in which the male terminal 100 can be engaged, and a tongue piece 123 whose base end portion 123b is continued from a backward end of an upper wall of the engaging part 122 and extends forward therefrom by way of a curved portion 123c. A contact 123a is provided near a forward end of the tongue piece 123.
In a terminal of miniature size such as a terminal employed in a micro current circuit, it has been a problem that the terminal may be deteriorated because of displacement of a contact position attributed to a minute sliding movement of the terminal which may be generated by an external factor such as a slide, a change of atmospheric temperature or so. In other words, in a connector for an automobile or the like provided with the terminal of miniature size, a contact portion between the male terminal and the female terminal may sometimes minutely slide in a longitudinal direction (back and forth direction) of the terminals or in a direction along a flat face of the male tab perpendicular thereto, resulting in a displacement of the contact position. Since the faces of both the terminals in contact with each other are gas tight, oxidation will be restrained, but the oxidation proceeds with time on other surfaces of the terminals. Therefore, when the contact position has been displaced as described above, such deterioration by the minute slide that the mating terminal may ride on an area on which an oxide film is formed, and may incur a decrease of electrical conductivity (faulty continuity) will be likely to occur.
As a countermeasure for this problem, it is requested that the contact of the tongue piece of the female terminal is made movable following the movement of the male terminal (so as not to be displaced with respect to the male terminal) which is caused by difference in thermal expansion or vibration of an engine, etc. In other words, it is requested that followability of the female terminal with respect to the male terminal is enhanced by making the contact forming portion of the tongue piece easily movable, so that the contact position between the male terminal and the female terminal may not be displaced.
On the other hand, it is also requested to appropriately increase contact load (contact pressure) for the prevention of a defective contact or chattering at the contact portion between the contact of the aforesaid tongue piece and the male terminal.
However, it has been difficult to satisfy both of the above requests at the same time, according to the conventional terminal structures as shown in FIGS. 6A, 6B, and 6C.
Describing more specifically, in the structure as shown in FIGS. 6A and 6B, a length from the base end portion 103b (113b) of the tongue piece 103 (113) to the contact 103a (113a) is relatively short, which is advantageous to increase the contact load by a restoring force corresponding to elastic deformation of this portion, when the male terminal is engaged therewith. However it has been difficult to enhance the followability to the movement of the male terminal 100, because the movement of the tongue piece is restricted.
On the other hand, in the structure as shown in FIG. 6C, in contrast with the structures as shown in FIGS. 6A and 6B, a length from the base end portion 123b of the tongue piece 123 to the contact 123a can be made relatively long, even though the female terminals have almost the same outer dimension. In this manner, the contact forming portion of the tongue piece 123 can easily move in the longitudinal direction of the terminals or in the direction along the flat face of the male tab perpendicular thereto, which is advantageous for enhancing the followability to the movement of the male terminal 100. However, with such a long structure of the tongue piece, the contact load tends to be decreased.
As described above, the increase of both the contact load and the followability of the female terminal to the movement of the male terminal has been a contradiction with each other in the conventional structures, and it has been difficult to satisfy both the requests at the same time.
In view of the above described circumstances, it is an object of the invention to provide a terminal structure which can satisfy, at the same time, both the request for enhancing followability of the contact to the movement of the male side conductor, and the request for increasing the contact load with respect to the male side conductor.
According to the invention, there is provided a terminal structure comprising an engaging part in a cylindrical shape which has at its forward end an opening for inserting a male side conductor so that the male side conductor can be engaged in the engaging part, and an elastic tongue piece having a contact which is arranged inside the engaging part so that the male side conductor to be engaged in the engaging part can be brought into contact with the contact of the tongue piece, characterized in that the elastic tongue piece is so constructed that its base end portion is fixed to a backward area of the engaging part, its distal end portion extends toward a forward area of the engaging part by way of a curved portion continued from the base end portion, and the tongue piece is provided with the contact at the distal end portion and a fulcrum portion at an intermediate position between the curved portion and the contact, the fulcrum portion being in contact with a wall face of the engaging part and slidable with respect to the wall face, whereby the tongue piece is supported at the fulcrum portion against a force applied in a direction in which the tongue piece is displaced by the insertion of the male side conductor.
With this structure, when the male side conductor is engaged in the engaging part, the contact of the above described tongue piece is pressed by the male side conductor in a direction perpendicular to the inserting direction of the male side conductor (in the longitudinal direction of the terminal: the back and forth direction). On this occasion, the tongue piece is supported at the fulcrum portion against a pressing force, and a portion extending from the fulcrum portion to the contact is elastically deformed to exert a restoring force to the contact portion between the contact and the male side conductor as the contact load. Therefore, the shorter the length from the fulcrum portion to the contact is, the more the aforesaid contact load is likely to be increased.
Moreover, in the engaged state of the male side conductor, when the male side conductor moves in the longitudinal direction of the terminal or in the direction along the flat face of the male tab perpendicular thereto by the difference in the thermal expansion or vibration, etc. with respect to the housing, the contact portion of the tongue piece also moves following the movement of the male side conductor. In this case, the above mentioned fulcrum portion can slide along the wall face of the engaging part, and a portion adapted to be displaced according to the force acting on the tongue piece will be formed at the area of the tongue piece from the base end portion to the contact. The longer this area is made, the more the contact of the tongue piece can easily move.
Therefore, by making the length of the tongue piece from the fulcrum portion to the contact relatively short, the contact load can be appropriately increased, and at the same time, by making the length of the tongue piece from the base end portion to the contact relatively long, the followability to the movement of the male side conductor can be enhanced.
The terminal structure according to the present invention is preferably a structure of a female terminal for conducting electrical connection with a male terminal as the male side conductor, characterized in that the base end portion of the elastic tongue piece is continued from a wall plate of the cylindrical engaging part in which the male terminal is adapted to be engaged, whereby the tongue piece and the engaging part are integrally formed of an electrically conductive metal plate. In this manner, the female terminal having the above described functions can be easily molded.
Further, the terminal structure according to the present invention may comprise a housing constituting the engaging part in which a flat cable as the male side conductor is adapted to be engaged, a slider adapted to be detachably inserted into the housing, and a terminal member having the elastic tongue piece arranged in the housing so that the flat cable may be clamped between the contact at the distal end portion of the tongue piece and the slider, characterized in that the base end portion of the tongue piece is fixed to the housing, and the fulcrum portion to be in contact with a wall face of the housing is provided at the intermediate position of the tongue piece between the curved portion continued from the base end portion and the contact.
In this manner, the contact load with respect to the flat cable as the male side conductor will be increased, and at the same time, the followability to the movement of the flat cable in the longitudinal direction can be enhanced.